In 1991 Central Sprinkler Co. demonstrated that extended coverage could be provided for ordinary hazard protection utilizing sprinklers with extra large orifices having diameters between about 0,625 and 0.64 providing K-factors of between about 11.2 and about 11.4. These sprinklers provided fire protection over extended coverage areas (greater than 130 sq. ft. per sprinkler) superior to that which was provided by then existing standard orifice, standard spray ceiling sprinklers over standard coverage areas (up to 130 sq. ft.). This improved fire protection could be achieved at reduced costs as the extended coverage areas permitted the use of fewer sprinkler runs and wider spacing of sprinklers on runs. Reduced cost provided an additional benefit. As the cost of sprinkler installations decline, they become more economically viable to install. Reduced costs not only led to savings by sprinkler system purchasers, it is believed this improved capability and reduced cost has fostered more widespread use of automatic ceiling sprinkler systems, at least for ordinary hazard protection.
Shortly after extended coverage was demonstrated for extra large orifice sprinklers, it was further demonstrated for very extra large orifice sprinklers having nominal (i.e. minimum) orifice diameters of between about 0.69 and 0.71 inches providing K-factors of between about 14.0 and about 14.5. These very extra large orifice extended coverage sprinklers provided coverage for the maximum permitted protection areas (up to 400 sq. ft.) at the lowest minimum required operating pressures (less than 35 psi) for the highest water densities (0.21 GPM/ft.sup.2). This made extended coverage ordinary hazard protection over the maximum permitted protection areas available at virtually all ordinary hazard installations without the need of auxiliary pumps to boost the pressure of water typically supplied to such installations.
Since the introduction of extended coverage ordinary hazard automatic sprinkler protection, improvements in such sprinklers have been directed to reducing their size for aesthetic purposes and reducing the minimum spacing permitted between sprinklers, which makes such sprinklers more easy to install. Minimum spacing is determined by "cold solder" testing. It is the minimum distance which can be used safely between identical sprinklers without the discharge from one sprinkler hitting the adjoining sprinkler and cooling that sprinkler to sufficiently prevent it from actuating when it should. Minimum permitted spacing for the first very extra large orifice, extended coverage ceiling sprinklers was 16 feet. That has been improved to 15 feet. This permits such sprinklers to be used at 16.times.16 ft. spacings in tiled ceiling buildings using standard 2.times.4 ft. tiles). Such sprinklers would be more versatile if, in addition to being capable of being used at maximum spacings of up to 20 feet, they could be used at minimum spacings less than 15 feet, particularly minimum spacings of 12 feet or even as low as 8 feet, both of which work well with standard tile ceilings.